(A) Field of the Invention
The present invention relates to a wafer protection method and system. More particularly, it relates to a wafer protection method and system using in chemical mechanical polishing process.
(B) Description of Related Art
Referring to FIG. 1, generally, as for present chemical mechanical polishing station, a wafer 11 is carried in place with a polishing head 13, and a retaining ring 12 is used to confine the wafer 11 to prevent the wafer 11 sliding out of the polishing head 13 during polishing. The polishing head 13 controlled by a robot arm (not shown) moves to above the polishing turntable and then processes wafer polishing with a polishing pad.
The prior art generally uses a spring sensor 14 or an optical sensor (not shown) to sense whether the wafer 11 exists in the polishing head 13 or not. While the wafer 11 is being polished, the spring sensor 14 compressed by the wafer 11 and a signal is transmitted to the station to ensure that the wafer 11 is in the polishing head 13. If the wafer 11 slides out of the polishing head 13, the spring sensor 14 would detect it by pressure release and send a shut down signal to the station for maintenance. However, the above manner has following disadvantages:
1. As a process or a recipe is modified, usually with pressure increase of the polishing head 13 for improvement of polishing rate and uniformity, the deflection of the wafer 11 or unstable pressure is often induced, resulting in error messages of the spring sensor 14.
2. During processing with the same recipe, due to the variation between each polishing head 13 and each spring sensor 14, the one sensitive to process will get error message easily.
3. After use for a long time, due to the aging of the parts of the station (e.g. the diaphragm, contacting the wafer 11, in the polishing head 13), the probability of error message will increase.
If the spring sensor 14 cannot detect the separate status of the wafer 11 and the polishing head 13, the collision of the slipped out wafer and the parts of the station will result in wafer be broken. Hence, this event increases the cost but also reduce the throughput due to the stop of the polishing process for station washing.
Another prior art uses a camera to monitor the whole polishing process, and which is watch by a staff at a remote control station. However, the above manner cannot halt the station instantly as the wafer slips out, and at most prevent the next coming wafer 11 from being continuously brought in the failed station causing even more damage. The artificial monitor manner will get error frequently, higher cost and management problem.
Summarized mentioned above, because the chemical mechanical polishing process is one of the extremely important processes in semiconductor manufacture, how to detect the sliding of the wafer 11 and immediately halt the station for cost reduction and throughput improvement is becoming a critical problem in semiconductor industry.
The object of the present invention is to provide a wafer protection method and system of the chemical mechanical polishing station for preventing wafer damage and reducing the probability of the station shut down due to error message. The present invention uses images obtained during polishing rather than the sensor of the polishing head used in prior art for wafer positioning. Hence, there is no sensor error message occurred, and more stable and higher quality judgment can be obtained. Further, the present invention entirely uses images for wafer position judgment. Hence, a sensor for detecting the beginning of the image analysis and identification is unnecessary.
An embodiment of the wafer protection method of the chemical mechanical polishing station of the present invention uses a camera to obtain a image in front of the rotation path of the polishing pad. If the brightness of the image exceeds a predetermined threshold, it means said wafer is away from the press of the robot arm, then a warning issued or the chemical mechanical polishing station is shut down.
An embodiment of the wafer protection system of the present invention includes a chemical mechanical polishing station, a polishing head, at least a camera, a computer and a remote I/O module. The chemical mechanical polishing station includes a polishing pad rotating in a specific direction. The polishing head is used to press a wafer to contact the polishing pad. The camera is used to obtain the image of the wafer in front of the rotation path of the polishing pad. The computer is used for analyzing the image obtained by the camera. If the computer finds any abnormal phenomenon, the remote I/O module will halt the operation of the chemical mechanical polishing station.